1. Field of the Invention
This invention relates to a method for maximizing reduction of delivery of nitrogen oxides, HCN and CO in tobacco smoke. In accordance with the invention, tobacco materials are contacted with an aqueous solution to form a tobacco extract. The extract is treated to remove potassium nitrate. Thereafter potassium ions are restored to the tobacco extract to a level approximating that originally present in the unextracted tobacco. By restoring potassium ions to the denitrated extract, a greater reduction in delivery of gas phase constituents is achieved relative to the amount of nitrate removed, than if the potassium ions are not restored to the tobacco materials. In addition, greater reduction in HCN and CO is observed.
2. Description of the Prior Art
Tobacco contains a number of nitrogen containing substances which during the burning of the tobacco yield various components in the smoke. Removal of some of these smoke components, such as the oxides of nitrogen, is considered desirable.
Nitrate salts, such as potassium, calcium and magnesium nitrates, are a major class of nitrogenous substances which are precursors for nitrogen oxides, especially nitric oxide. These nitrate salts are normally found in great abundance in burley tobacco stems and strip, in flue-cured tobacco stems to a lesser degree, and in reconstituted tobaccos which utilize these components. Attempts have been made to reduce or remove the nitrate from these tobaccos to bring about a significant reduction in the oxides of nitrogen delivered in their smoke. Among the techniques which have been employed to this end are extraction methods whereby the nitrates are removed from the tobacco material.
In accordance with extraction techniques, tobacco materials are generally contacted with water. In this manner an extract containing the tobacco solubles including the nitrates is formed. The extract is collected and may be discarded or may be treated to remove the nitrates. The denitrated extract may thereupon be reapplied to the fibrous insoluble tobacco material from which it was originally removed.
Although extract treatment methods seek to minimize the removal of materials other than nitrates from the tobacco and thereby avoid affecting the subjective characteristics of the tobacco or its filling capacity, burn qualities and the like, other materials are in fact removed by such methods. For example, the nitrates are commonly removed as potassium salts. Specifically, U.S. Pat. Nos. 4,131,118 and 4,131,117 describe a denitration process wherein potassium nitrate is crystallized from an aqueous tobacco extract followed by reapplication of the denitrated extract to the tobacco. In U.S. Pat. No. 3,847,164 denitration is effected by means of ion-retardation resins which retard ionic material, specifically potassium nitrate, in tobacco extracts, while non-ionic constituents pass unaffected. Thus, these methods remove not only nitrate ions, but also potassium ions.
In addition to denitration, extraction processes are employed where removal of other tobacco components is desired. For example, U.S. Pat. No. 3,616,801 describes a process for improving the tobacco burn properties, smoke flavor and ash by controlling the ion content of the tobacco. In accordance with the process therein disclosed the proportion of metallic ions in an aqueous tobacco extract is adjusted, followed by reapplication of the treated extract to the tobacco. Among the treatments suggested for adjusting the metal ion content are ion exchange and membrane electrodialysis. Removal of potassium ions and their replacement with ammonium, hydrogen, calcium or magnesium ions are particularly desirable in the practice of this process. Levels of other ions including nitrate may also be adjusted to alter the tobacco properties. In Example 6, over 50% of both nitrate and potassium ions were removed by means of electrodialysis.
The addition of potassium salts to conventional, unextracted tobacco materials has been suggested for a variety of reasons. For example, in German Offenlegungsschrift No. 2,632,693, KNaCO.sub.3.6H.sub.2 O, K.sub.2 CO.sub.3 and glycols may be added to tobacco stems to a pH of 8-9 and thereafter the stems are mixed with leaf filler. This tobacco stem treatment is said to decrease the smoke content of aldehydes and condensate. Potassium phosphates are disclosed as having humectant properties when added to tobacco at a level of at least 0.5% by weight, according to U.S. Pat. No. 2,776,916. U.S. Pat. No. 467,055 discloses a process for improving the burning qualities of poor grade tobaccos by applying thereto potassium carbonate. The treatment is also said to render the tobacco decay proof.
In U.S. Pat. No. 2,972,557 smoking tobacco is treated with an alkali metal compound such as sodium bicarbonate, potassium bicarbonate or potassium ruthenate at an approximate level of 2 to 8% to produce a smoking product which burns below a temperature of 800.degree. F. According to the inventor, the temperature control substances reduce the amount of compounds that may be volatilized and released into the smoke.
In U.S. Pat. No. 3,126,011 there is disclosed a process for reducing high-molecular weight compounds resulting from pyrolysis of tobacco materials. Incombustible solids capable of melting endothermically at a temperature at or below the burning temperature of the tobacco are suggested and include salts of borates, phosphates and silicates, and hydrates thereof with cations selected from potassium, lithium, and sodium. The salts are applied to tobacco at a level between about 3 and 10% by weight.
In U.S. Pat. No. 2,914,072 there is described a process for upgrading poor quality tobacco and particularly tobacco having increased alkalinity of the smoke. According to the inventor, primary and secondary catalyst in combination with aliphatic acids promote a greater degree of thermal destruction of nitrogen bases thereby reducing alkalinity of the smoke. Salts of cobalt, manganese, nickel, copper, chromium and silver comprise primary catalyst while salts of potassium, magnesium, barium and sodium comprise secondary catalyst. Application to tobacco of about 2% of each class of salts apparently produce satisfactory results.
In some instances tobacco is extensively extracted and the resultant extract discarded. No attempt is made to selectively remove certain constituents of the extract and then return the extract to the fibrous tobacco residue. For example, in U.S. Pat. No. 2,122,421, tobacco leaf ultimately used for cigar wrappers is subjected to a "steeping or scrubbing" action followed by further extraction in an aqueous-alkaline bath generally at a pH between 8 to 11. According to the inventor, the burning qualities of the tobacco are usually completely destroyed by the above-described treatment. In order to restore burn properties, a salt such as potassium acetate is added to the depleted fibrous tobacco residue by immersing the residue in an aqueous bath containing approximately 12.5 pounds potassium acetate per gallon of solution.
In accordance with U.S. Pat. No. 2,029,494, tobacco leaf is subjected to extraction in a nitric acid-containing bath whereby substantially all of the naturally occurring gums, oils, nicotine and mineral matter including salts are removed. The "skeleton leaf" consisting essentially of the woody and starch components is then treated to impart the desired color, flavor, aroma, ash and smoking properties. A solution containing equal portions of a tobacco extract derived from tobacco stems; a mineral mixture containing potassium acetate, potassium nitrate and calcium acetate; and a third solution containing potassium carbonate, is prepared and applied to the previously extracted tobacco leaf. The thus treated leaf is then used as a cigar wrapper.
It is generally recognized that discarding tobacco extracts results in the loss of valuable tobacco solubles, many of which contribute substantially to the subjective characteristics of the tobacco. The process of the present invention is advantageous in that tobacco is subjected to aqueous extraction and the resultant extract is denitrated whereby potassium nitrate is predominantly removed while maintaining other desirable tobacco solubles intact. Thereafter potassium ions are restored to the potassium-depleted tobacco to a level approximating that originally present prior to extraction.
A proportionately greater reduction in delivery of nitrogen oxides in tobacco smoke relative to degree of nitrate removal is achieved than when the potassium ions are not restored.